GSoC 2018: SymPy - Week 2

I started the week by finalizing the PR #14725. The PR has been merged successfully. Fast Walsh Hadamard Transform (fwht) will be added along with XOR Convolution at a later point of time.

Late this week, I started working on the convolution module PR #14745 with the aim of adding the following along with appropriate tests.

Convolution using Fast Fourier Transform (convolution_fft)

Convolution using Number Theoretic Transform (convolution_ntt)

General Convolution method (convolution)

Kalevi and Aaron suggested using convolution as the name for the methods instead of conv.
I had a detailed discussion with Kalevi regarding the API of the methods, the need to tie convolution with DFT (Discrete Fourier Transform), and handling the cyclic convolution case.